1. Field of the Invention
The present invention relates to a rotational position detecting apparatus for detecting a reference rotational position such as a top dead center position of an internal combustion engine on the basis of detection signals outputted from a rotational angle sensor and an in-cylinder sensor.
2. Description of Related Art
Generally, as shown in FIG. 5A, the rotational position of an internal combustion engine is detected by use of an NE sensor (rotational angle sensor) 58 which detects projections (or slots) of a pulser 52 rotating synchronously with a rotating shaft (or crankshaft) of an internal combustion engine.
The pulser 52 having a circular disc shape is formed with projections (or slots) 54 evenly spaced along its circumferential direction. When the pulser 52 rotates with the rotation of the internal combustion engine, the NE sensor 58 outputs a pulse-like rotation angle signal for each predetermined rotation angle of the internal combustion engine as shown in FIG. 5B.
By counting the rotation angle signals outputted from the NE sensor 58, it is possible to determine the rotational position of the internal combustion engine for each one cycle (720° CA) on the basis of which various timings (fuel injection timing, for example) of the internal combustion engine are controlled.
To be more precise, to determine a reference rotational position of the internal combustion engine such as a top dead center position, it is necessary to form, in addition to the projections 54 (or slots), a tooth missing portion 56 or an additional projection in the pulser 52, as shown in FIG. 5A.
However, there has been a problem that the rotational position of the internal combustion engine cannot be correctly determined due to manufacturing tolerances of the pulser teeth or projections 54 (see FIG. 5C), or mounting tolerances of the NE sensor 58 (see FIG. 5D), which cause the phases or intervals of the rotation angle signals outputted from the NE sensor 58 to deviate from nominal values.
Accordingly, to enable correctly detecting the rotational position of the internal combustion engine even if the phases or intervals of the rotation angle signals outputted from the NE sensor 58 deviate from nominal values, it is proposed to detect in-cylinder pressure of a cylinder when the internal combustion engine is in a non-combusting condition, and determine that the cylinder is at a reference rotational position when its in-cylinder pressure reaches its maximum value, assuming that the cylinder is at the top dead center (may be referred to as “TDC” hereinafter) as the reference rotational position when the in-cylinder pressure reaches its maximum value (see FIG. 5E ). For more details, refer to Japanese Patent application Laid-open No. 11-210546, or Japanese Patent Publication No. 3-19500, or Japanese Patent Publication No. 64-11819.
However, noise occurred around the internal combustion engine is likely to superimpose on the detection signal indicative of the in-cylinder pressure outputted from the in-cylinder pressure sensor. Accordingly, since the rotational position at which the in-cylinder pressure obtained from the detection signal outputted from the in-cylinder sensor reaches the maximum value may deviate from the true reference rotational position (TDC position) at which the in-cylinder pressure actually reaches the maximum value (see FIG. 5F), causing detection error of the rotational position.
It may occur that the detection signal outputted from the in-cylinder sensor is subjected to a filtering process to remove the noise therefrom, and the rotational position at which the in-cylinder pressure reaches the maximum value is detected on the basis of the detection signal which has been subjected to the filtering process.
However, in this case, since a phase delay occurs in the detection signal when it is subjected to the filtering process, it is not possible to detect the TDC position with sufficient precision, nor to sufficiently reduce the detection error of the rotational position.